The invention relates to a clutch mechanism for a screw tightening machine in which improvement is made to prevent noise and reduce shock at the time the clutch is engaged and released.
As shown in FIGS. 9(a) and 9(b), a clutch mechanism for a screw tightening machine such as an electric screwdriver of this type is generally constructed so that trapezoidal clutch claws 30 are formed on the surface of a screw tightening machine main body a and the surface of a driver bit b, both surfaces opposing each other. These clutch claws 30 are meshed with each other so that the clutch mechanism is engaged to transmit motive power and are disengaged from each other so that the clutch mechanism is released to stop the transmission of the motive power.
Each clutch claw 30 has such a section as shown in FIG. 9(b). That is, the mating surfaces are sloped. Therefore, to maintain the meshed condition, the screw tightening machine main body must be urged in the screwing direction.
However, the conventional clutch mechanism has following difficulties. That is, if, e.g., a poor scaffolding does not allow the operator to continuously apply strong urging load to the screw tightening machine and the clutch claws are therefore disengaged from each other in the course of screw tightening operation, then the clutch claws collide against each other to make noise continuously or to wear the corners of the clutch claws. Moreover, when the clutch engaging operation alternates with the clutch releasing operation, shock against the screw tightening machine before and after such operations increases, thereby impairing operating and handling ease.